The C-terminal half of the light or the heavy chain of an immunoglobulin molecule that is identical in all antibodies of the same isotype. The sequence of the variable region determines the antigen specificity. Heavy chains α, γ, and δ (in IgA, IgG, and IgD) have a constant region of ~450 aa with three tandem Ig-type domains, and a hinge region; heavy chains μ and ε (in IgM and IgE) have four immunoglobulin domains in the constant region. The constant regions of light chains are smaller (~215 aa).
Subjects: Chemistry — Medicine and Health.